Process for preparing an olefin oxide using a multi-lobed porous ceramic body

ABSTRACT

A carrier having at least three lobes, a first end, a second end, a wall between the ends and a non-uniform radius of transition at the intersection of an end and the wall is disclosed. A catalyst comprising the carrier, silver and promoters deposited on the carrier and useful for the epoxidation of olefins is also disclosed. A method for making the carrier, a method for making the catalyst and a process for epoxidation of an olefin with the catalyst are also disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/428,009 filed Dec. 29, 2010.

BACKGROUND OF THE INVENTION

This invention relates to porous ceramic bodies having a contoured shapethat is particularly suitable for use as a carrier for catalyticallyactive material. The combination of carrier and active material mayfunction as a catalyst when randomly disposed within a reactor tubewhich is useful in the manufacture of chemicals such as ethylene oxide.

Ethylene oxide, which may be abbreviated herein as EO, is an importantindustrial chemical used as a feedstock for making such chemicals asethylene glycol, ethylene glycol ethers, alkanol amines and detergents.One method of manufacturing ethylene oxide is by the catalyzed partialoxidation of ethylene with oxygen. There are continuing efforts todevelop catalysts that can improve the operating efficiency of suchethylene oxide manufacturing processes. Some of the desirable propertiesof an ethylene oxide catalyst include good selectivity, good activity,and long catalyst life. It is also important that the catalyst as loadedin the reactor tubes results in as relatively low pressure drop acrossthe EO reactor as is possible. Achieving significant pressure dropimprovement with higher packing density would enhance the stability ofan EO catalyst in existing EO plants and would allow for the design ofmore efficient new EO plants.

The typical catalysts employed to make EO comprise silver and othermetals and promoters on a carrier, typically an alpha alumina carrier.These silver catalysts are described in many US and foreign patents,including, among others, U.S. Pat. No. 4,242,235; U.S. Pat. No.4,740,493; U.S. Pat. No. 4,766,105; U.S. Pat. No. 7,507,844; U.S. Pat.No. 7,507,845; U.S. Pat. No. 7,560,577; U.S. Pat. No. 7,560,411; U.S.Pat. No. 7,714,152; US 2008/0081920; US 2008/0306289; US 2009/0131695and US 2009/0198076. The shape of the catalyst takes the shape of thecarrier. The shape of a carrier may be characterized by describing oneor more of the following features: length, outer diameter, innerdiameter; ratio of length to diameter; radius of an exterior wall;radius of an end surface; shape when viewed from an end; and shape whenviewed from a side. The most common commercially available carrier shapeis a small cylinder pellet shape with a hole in the center of thepellet. See, e.g., U.S. Pat. No. 7,259,129, which disclosure is hereinincorporated by reference. In the '129 patent the support material hasspecific physical properties and is preferably formed into a shapedagglomerate of the support material having a hollow cylinder geometricconfiguration or structure with a relatively small internal diameter. Incontrast, U.S. Pat. No. 4,441,990 discloses hollow shaped catalyticextrudates which may be employed in catalytically promoted processesincluding hydrocarbon processing operations. The shapes includeessentially rectangular shaped tubes, and triangular shaped tubes incross section. One embodiment is characterized by having bulbousprotrusions around the external periphery. Wall thicknesses from about ⅛inch, 1/10 inch, or even 1/25 inch or less are disclosed. US2009/0227820 discloses a geometrically shaped refractory solid carrierin which at least one wall thickness of the carrier is less than 2.5 mm.U.S. Pat. No. 6,518,220 discloses shaped catalysts for heterogeneouslycatalyzed reactions in the form of hollow cylinders or annular tabletswhose end faces are rounded both to the outer edge and to the edge ofthe central hole, so that they have no right-angled edges. Onemodification of such a catalyst shape comprises a pellet where therounded edges are only on the outer edge of the pellet, and the inneredge of the central hole does not comprise rounded edges. U.S. Pat. No.6,325,919 discloses catalyst carriers composed of a refractory inorganicoxide having a rotationally symmetrical shape having a hollow portion,such as a doughnut shape. An outer peripheral surface and the innerperipheral surface separating the hollow portion are linked by curvedsurfaces, and the height of the carrier along the rotational symmetryaxis is less than the outer diameter of the carrier. EP 1,184,077discloses a porous refractory carrier in the form of an angularextrudate with rounded edges. WO 03/013725 discloses elongated shapedtrilobal particles. U.S. Pat. No. 2,408,164 discloses numerous shapedcatalyst including planar, cylindrical with a central opening and aplurality of parallel grooves disposed in the outer periphery, andcylindrical with several parallel passageways formed therein. U.S. Pat.No. 4,645,754 discloses catalysts made from a carrier that is in theshape of Intalox saddles or Berl saddles. Other shapes that have beenmentioned in the patent art include spheres, tablets, rings, spirals,pyramids, cylinders, prisms, cuboids, cubes, etc. See, for example: USPublished Patent Applications 2008/0015393, 2008/0255374, 2009/0041751,2009/0227820; U.S. Pat. Nos. 5,155,242 and 7,547,795; and internationalpublication WO 2004/014549.

However, there continues to be a need for improved catalysts havingbetter performance in the reactor than currently are available. Thepresent invention provides carriers and catalysts that enable such animprovement.

SUMMARY

A carrier of the present invention provides for improved performance ina reactor by combining a multi-lobal cross-sectional configuration withnon-uniform rounding at the intersections of the carrier's ends andwall. A catalyst of the present invention is a novel combination ofcatalytic components and a carrier of this invention.

In one embodiment, this invention is a porous ceramic body comprising afirst end, a second end, and a wall disposed between the ends. The wallcomprises at least three lobes formed in the length of the wall. Thefirst end and wall intersect one another at a first circumferential linehaving a non-uniform radius of transition.

In another embodiment, the invention is a catalyst that includes silverand promoters useful for the epoxidation of ethylene deposited on aspecifically shaped porous ceramic body having a first end, a secondend, and a wall disposed between the ends. The wall comprises at leastthree lobes formed in the length of the wall. The first end and wallintersect one another at a first circumferential line having anon-uniform radius of transition.

According to another aspect of the invention, a method is provided formaking the catalyst of this invention. Suitably, the method involvesproviding a carrier of this invention and impregnating the carrier witha silver-containing solution such that the amount of silver metal on thecarrier exceeds 8 weight percent of the weight of the catalyst.Preferred amounts of silver are between 10 and 30 weight percent of theweight of the catalyst. The silver impregnated shaped carrier is thenheat treated to provide the catalyst, for example in a temperature rangeof from 100° to 500° C., preferably from 150° to 320° C.

According to yet another aspect of the invention, a packed catalyst bedis provided which is formed from catalyst particles comprising silversupported on a carrier of this invention, which catalyst bed has asilver loading of at least 50 kg silver/m³ of catalyst bed.

According to yet another aspect of the invention, the catalyst made bythe above-described method, or the above described catalyst bed is usedin a process for manufacturing ethylene oxide by contacting thecatalyst, under suitable epoxidation process conditions, with a feedstream that comprises ethylene and oxygen.

Further, the invention provides a method of using ethylene oxide formaking ethylene glycol, an ethylene glycol ether or an 1,2-alkanolaminecomprising converting ethylene oxide into ethylene glycol, the ethyleneglycol ether, or the 1,2-alkanolamine, wherein the ethylene oxide hasbeen obtained by the process for preparing ethylene oxide according tothis invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a first embodiment of a carrier of thisinvention;

FIG. 2 is an end view of a second embodiment of a carrier of thisinvention;

FIG. 3 is a side view of a the carrier shown in FIG. 2;

FIGS. 4A and 4B depict an end view and a perspective view of a thirdembodiment of a carrier of this invention;

FIGS. 5A and 5B depict an end view and a perspective view of a fourthembodiment of a carrier of this invention;

FIGS. 6A and 6B depict an end view and a perspective view of a fifthembodiment of a carrier of this invention;

FIG. 7 depicts a conventional ring shaped carrier and is labeled PriorArt; and

FIGS. 8A-8J depict cross-sectional views often carriers of thisinvention.

DETAILED DESCRIPTION

As used herein, the phrases “porous ceramic body”, “carrier” and“support” are used interchangeably. The word “catalyst” refers to acarrier that includes a catalytically active material deposited onto thecarrier. Because the thickness of the catalytically active material isvery small relative to the width of the carrier, the apparent shape ofthe carrier and the shape of the catalyst are essentially identical.

A “porous ceramic body” may refer to an elongated rod like body having amulti-lobal cross sectional shape—i.e., when viewed from either end, theend faces of the porous body have a multi-lobal shape and the body has acertain height which may also be described as its length. Examples ofmulti-lobal shaped carriers are shown, for example, in FIGS. 8A to 8J.One embodiment of a multi-lobal porous ceramic body is a hollowquadrilobal shaped carrier. The phrase “quadrilobal shaped” refers tothe carrier's cross-sectional view having four non-triangularly, forexample semi-circularly, shaped extensions on the circumference thereof.Perspective views of hollow quadrilobal shaped carriers are shown, forexample, in FIGS. 1 and 5B. The phrase “hollow quadrilobal shapedobject” refers to a cross-section having at least one passagewaytherethrough, with four non-triangularly, for example semi-circularly,shaped extensions on the circumference thereof.

Porous ceramic bodies used as carriers for catalytically active materialhave numerous physical and chemical characteristics that collectivelyand individually influence the selectivity, longevity, yield anddurability of the catalyst when disposed in a chemical reactor. Theporous body's physical and chemical characteristics may also impact themanufacturability of the carrier and the catalyst. Numerous patents andtechnical articles have focused on improving the catalyst by modifyingcharacteristics such as the carrier's surface area, pore sizedistribution and morphology, which may be referred to herein as thecarrier's micro physical characteristics. In other publications, thecarrier's macro physical characteristics, such as its length, outerdiameter and inner diameter, have been described. In yet otherpublications, the relationships between the carrier's macro physicalcharacteristics and the reactor tube's inside diameter have beendescribed. The inventor of the invention claimed herein has discoveredthat the total performance of the catalyst, which includes: preparationof the carrier and preparation of the catalyst; selectivity andlongevity of the catalyst; pressure drop within the reactor; and thecarrier's resistance to attrition and breakage, may all be favorablyinfluenced by shaping the carrier to include multiple lobes and roundedcorners having a non-uniform radius of transition. The combination ofrounded corners and multiple lobes may be used to increase the packingdensity of the catalyst in the reactor relative to conventional carrierrings with non-rounded corners. An increase in packing density may besignificant because the quantity of silver per unit volume of thereactor increases as the packing density of the carrier increases.Increasing the quantity of silver per unit volume of the reactor mayimprove the reactor's throughput which may be referred to herein as theyield. Furthermore, the combination of rounded corners and multiplelobes may also cooperate to provide less tortuous passageways for theflow of fluids through the catalyst bed in the reactor, relative to abed of carrier rings with non-rounded corners, which avoids asignificant increase in pressure drop despite the increase in thecatalyst's packing density. The combination of rounded corners andmultiple lobes also eliminates the portions of the catalyst that aremost readily attrited during the procedures used to manufacture thecatalyst. Minimizing both the pressure drop in the reactor and theamount of attrited particles while increasing the catalyst's packingdensity allows the potential impact of the carrier's micro physicalcharacteristics to be more fully utilized thereby resulting in improvedselectivity and longevity which collectively improve the reactor'seconomic performance. In addition to characteristics that enhance theselectivity and longevity of the catalyst, the carrier should also havesufficient mechanical strength to prevent breaking during the catalystmanufacturing process and the process of loading the catalyst into thereactor. In some embodiments, the carrier has at least one passagewaydisposed through the length of the carrier. In some embodiments thecarrier may have 2 to 4 passageways. In some embodiments the carrier mayhave one passageway for each lobe. If the carrier has an even number oflobes, the carrier may have an even number of passageways. Similarly, ifthe carrier has an odd number of lobes, the carrier may have an oddnumber of passageways. Furthermore, the number of lobes and the numberof passageways do not need to be the same. The passageways may besymmetrically or asymmetrically disposed about the carrier's centralaxis which, by definition, extends from the carrier's first end to itssecond end and is located at the center of the carrier. One of theadvantages of a hollow “multi-lobal” shaped carrier is that the carriermay have good mechanical strength, which may be quantified by measuringthe carrier's side crushing strength (SCS) and its bulk crushingstrength (BCS), despite the presence of a passageway through thecatalyst. The use of multiple passageways may be preferred to the use ofa single passageway that has the same cross-sectional surface area asthe multiply passageways combined, because the multiple passagewaysprovide for a smaller wall thickness and thus minimize the impact ofdiffusion limitations through the carrier. Still further, catalyst withmultiple passageways may also be easier to manufacture than catalystwith a single opening. In one embodiment and as shown in FIG. 4A, thecarrier is a trilobal shape wherein the lobes are truncated on the outerportion of the lobes and the number of passageways is equal to thenumber of lobes.

Features and characteristics of the carriers and catalysts of thisinvention, and the methods to manufacture the same, will now bedescribed.

Shown in FIG. 1 is a quadrilobal carrier 20, which may also be describedherein as a quadrilobate carrier that includes first end 22, second end24 and wall 26. Carrier 20 includes first lobe 28A, second lobe 28B,third lobe 28C and fourth lobe 28D. The intersection of first end 22 andwall 26 form first circumferential line 30 which is denoted by thedotted line in FIG. 1. The first circumferential line is defined as acontinuous series of points around the carrier where the surface offirst end 22 transitions to the surface of wall 26. The radii oftransition from the first end to the wall is non-uniform along thecircumferential line because the transition from the first end to thewall has been rounded more in some locations and not rounded or roundedvery little in other locations thereby creating the non-uniform radiusof transition along the circumferential line. The largest radii oftransition is at apex 32 of each of the lobes and the smallest radii oftransition is at nadir 34 in the valleys 35 formed between two lobes.Between one of the largest radii of transition and an adjoining smallestradii of transition the radii of transition varies along thecircumferential line. Carrier 20 includes first passageway 36, secondpassageway 38 and third passageway 40. Each passageway extendscompletely through the carrier thereby allowing fluids, includingliquids used in the catalyst preparation process and gases used in areactor tube, to flow into and through the carrier from one end of thecarrier to the opposite end of the carrier. First passageway 36 iscircular. Second passageway 38 is oval shaped and the longest axis 42 ofthe oval aligns with the apexes of lobes 28B and 28D. Third passageway28C is a six sided polygon. The radius of lobe 28B is identified byarrow 44 and the radius of the valley between lobes 28A and 28D isidentified by arrow 46. Although not shown in FIG. 1, second end 24intersects wall 26 at a second circumferential line which is defined asa continuous series of points around the carrier where the surface ofsecond end 24 transitions to the surface of wall 26.

To determine the radius of transition for the leading edge of acarrier's lobe, an optical comparator can be used to illuminate thecarrier thereby creating an image that can be measured. However, todetermine the minimum radius of transition at a carrier's valley, thecarrier can be cross sectioned to expose the valley and the radius canbe measured using an optical comparator.

As used herein, a carrier is considered to have a non-uniform radius oftransition if a carrier's largest radius of transition at theintersection of the wall and end is at least three times greater thanthe carrier's smallest radii of transition at the intersection of thesame wall and end. For example, if the largest radius of transition atthe leading edge of a carrier's lobe is 6.0 mm then the smallest radiusof transition at an adjoining valley should be 2.0 mm or less.

While the location of the passageways through the porous ceramic bodymay not be critical in some applications, providing a plurality ofpassageways symmetrically spaced around the end of the body, such thatthe distances from a passageway to the closest surface of the wall isminimized and standardized, may facilitate preparation of the catalystby minimizing the amount of time needed to diffuse liquid used in thecatalyst preparation process into and through the carrier. The shape ofall the passageways may be identical or, as shown in FIG. 1, thepassageways may have different shapes.

Shown in FIGS. 2 and 3 are an end view and a side view, respectively, ofa quadrilobal catalyst that contains a passageway therethrough. Thepassageway has an inside diameter B. The catalyst contains four roundlobes. D refers to the diameter of the overall catalyst. R refers to theradius of the individual round lobe. H refers to the height of thecatalyst. In one embodiment, the present invention may be a catalystcomprising silver and promoters useful for the epoxidation of olefinsdeposited on a multi-lobal shaped carrier having between 3 and 8 lobeswith a geometric configuration wherein the ratio of D divided by R isbetween 3 and 8, and the ratio of H to D is between 0.5 and 3. It hasbeen found particularly advantageous to use a shaped catalyst whereinthe ratio of H to D is in the range of from 0.8 to 1.5. In FIG. 2, theoverall diameter of the catalyst is approximately four times the radiusof the individual lobes (R). The range of R is about 0.1 millimeters onthe low side and nearly infinite or “flat” on the high side. PreferablyR is about 1 to 20 millimeters; more preferably about 1 to 10millimeters. The overall diameter D of the catalyst is preferablybetween 2 and 50 millimeters; most preferably between about 4 and 20millimeters. The range for H is about 2 to 50 millimeters; preferablyabout 4 to 20 millimeters; preferably the ratio of H to D is about 1to 1. The diameter (bore size) of hole B varies from 0.5 to about 5millimeters, preferably between about 1 and about 4 millimeters. Thebore size may be between about 0.1 to 0.9 times the diameter (D) of thecatalyst; preferably between about 0.2 and 0.6 times the diameter of thecatalyst. While only one hole is shown in FIG. 3, it is contemplatedthat one or more passageways may be employed. In a preferred embodiment,there is one passageway for each lobe.

Shown in FIGS. 4A and 4B are an end view and a perspective view,respectively, of a three lobed carrier having three passageways.

Shown in FIGS. 5A and 5B are an end view and a perspective view,respectively, of a four lobed carrier having a single passageway.

Shown in FIGS. 6A and 6B are an end view and a perspective view,respectively, of another four lobed carrier having a single passageway.

FIG. 7 is a perspective view of a prior art carrier that has no lobesand the corners of the carrier are not rounded.

FIGS. 8A through 8J disclose cross-sectional views of severalmulti-lobed carriers having at least three lobes and between one andfive passageways. The shape designated A has four truncated lobes andtwo oval shaped passageways. The shape designated B has four lobes and agradual rounded intersection of the lobes. The shape designated C hasfour semi-circular lobes. The shape designated D has five semi-circularlobes. The shape designated E has four lobes and a gradual roundedintersection of the lobes. The shape designated F has four truncatedlobes and three passageways. The shape designated G has four extendedlobes. The shape designated H has four extended semi-circular lobes. Theshape designated I has five lobes and a rounded intersection of thelobes. The shape designated J has four semi-circular lobes including arounded intersection of the lobes.

Typical prior art preparation of an alpha alumina carrier involvesmixing alpha alumina powder(s) with a combination of bonding agents,extrusion aids, water, fluxing agents, other alumina materials andoptionally, burnout materials to provide a manually malleable mixture.Detailed descriptions of processes that can be used to make suitablemixtures can be found in U.S. Pat. No. 6,831,037 and U.S. Pat. No.7,825,062. A suitable mixture may then be extruded through anappropriately shaped die to provide an extrudate having three or morelobes formed in the wall of the extrudate and parallel to the centralaxis of extrusion. The extruate may then be cut into a plurality ofindividual unfired, carrier precursors commonly known as greenware. Theextrudate may be cut by a fast moving blade which cuts through theextrudate essentially perpendicular to the direction of extrusion. Theresulting carrier precursors have a first end, a second end and the wallwhich extends between the first end and the second end. The ends areessentially parallel to one another and perpendicular to the wall. Thefirst end and wall intersect at a right angle which inherently defines asmall, uniform radius of transition. The radius of transition defines acircumferential line which has a uniform radius of transition.Similarly, the second end and wall intersect at a right angle whichinherently defines a small, uniform radius of transition that is equalto the radius of transition at the intersection of the first end andwall. A plurality of the carrier precursors may then be tumbled in acontainer, such as a rotating tube, that allows the precursors tocontact one another and/or the sides of the container. During thetumbling process, the carrier precursors contact one another and theleading edges of the lobes are compressed thereby rounding the edges ofthe lobes. Due to the multi-lobe design of the precursor, the leadingedge of the precursor is compressed the greatest amount and the valleysbetween the lobes are not compressed or are compressed very little.Consequently, the leading edges of the lobes have the largest radius oftransition and the valleys between the lobes have the smallest radius oftransition. Between the leading edge of a lobe and the valley, theprecursor's radius of transition may be larger than the smallest radiusof transition but smaller than the largest radius of transition. Theamount that the leading edge is compressed, and thus the leading edge'sradius of transition, may be controlled by adjusting factors such as thelength of time the precursor is tumbled and the speed that the containeris rotated. The precursors having the non-uniform radius of transitionare then dried to remove water and fired at high temperatures to formthe carrier body. High temperatures (greater than 1200° C.) are requiredto affect the proper bonding of the alpha alumina particles to oneanother and to provide a carrier having the desired surface area.Instead of using an extrusion process to form carriers of thisinvention, a suitable mixture may be disposed into a cavity and thecarrier may be formed by pressing the mixture to the desired shaped.Carriers that have been formed by pressing may be manufactured with thedesired rounding at the carrier's end to wall interfaces and thereforedo not need to tumbled in order to impart the desired non-uniform radiusof transition at the intersections of the carrier's ends and wall.

A carrier of this invention may be made from any porous refractorymaterial that is relatively inert in the presence of ethylene oxidationfeeds, products and reaction conditions provided such material has thedesired physical and chemical properties. Generally, the materialcomprises an inorganic material, in particular an oxide, which caninclude, for example, alumina, silicon carbide, carbon, silica,zirconia, magnesia, silica-alumina, silica-magnesia, silica-titania,alumina-titania, alumina-magnesia, alumina-zirconia, thoria,silica-titania-zirconia and various clays.

The preferred porous refractory material comprises alumina preferably ofa high purity of at least 90 weight percent alumina and, morepreferably, at least 98 weight percent alumina. Frequently, therefractory material comprises at most 99.9 weight percent, morefrequently at most 99.5 weight percent alumina. Among the variousavailable forms of alumina, alpha-alumina is the most preferred.

After firing, the carrier's micro physical characteristics may have amean pore diameter of 0.3 to 15 μm, preferably 1 to 10 μm; and amonomodal, bimodal or multimodal pore size distribution as determined bymercury intrusion to a pressure of 3.0×10⁸ Pa using a MicrometricsAutopore 9200 model (1300 contact angle, mercury with a surface tensionof 0.473 N/m, and correction for mercury compression applied). Thefollowing are some of the many options for carrier pore distribution.First, the carrier may have a surface area of at least 1 m²/g, and apore size distribution such that pores with diameters in the range offrom 0.2 to 10 μm represent at least 70% of the total pore volume andsuch pores together provide a pore volume of at least 0.27 ml/g,relative to the weight of the carrier. Second, a carrier may have amedian pore diameter of more than 0.5 μm, and a pore size distributionwherein at least 80% of the total pore volume is contained in pores withdiameters in the range of from 0.1 to 10 μm and at least 80% of the porevolume contained in the pores with diameters in the range of from 0.1 to10 μm is contained in pores with diameters in the range of from 0.3 to10 Pun. Third, a carrier having at least two log differential porevolume distribution peaks in a pore diameter range of 0.01-100 μm and atleast one peak of the above peaks is present in a pore diameter range of0.01-1.0 μm in the pore size distribution measured by mercury intrusion,wherein each peak is a maximum value of the log differential pore volumedistribution of 0.2 cm³/g or larger. Fourth, a carrier having a bimodalpore size distribution, with a first mode of pores which has a meandiameter ranging from about 0.01 m to about 5 μm, and a second mode ofpores which has a mean diameter ranging from about 5 μm to about 30 μm.Fifth, a carrier having a pore volume from pores with less than 1 micronin diameter of less than 0.20 ml/g, a pore volume from pores withgreater than 5 micron in diameter of less than 0.20 ml/g, and a porevolume from pores between 1 micron in diameter and 5 microns in diameterat least 40 percent of a total pore volume. Furthermore, the surfacearea of the carrier, as measured by the B.E.T. method, can be in therange of from 0.03 m²/g to 10 m²/g, preferably from 0.05 m²/g to 5 m²/gand most preferably from 0.1 m²/g to 3 m²/g. Suitably, the surface areais at least 0.5 m²/g. The B.E.T. method of measuring surface area hasbeen described in detail by Brunauer, Emmet and Teller in J. Am. Chem.Soc. 60 (1938) 309-316, which is incorporated herein by reference.

In addition to the carrier having a specific geometric configuration,incorporated onto the carrier is at least a catalytically effectiveamount of silver and, optionally, one or more promoters and, optionally,one or more co-promoters. Thus, the inventive catalyst comprises acarrier, a catalytically effective amount of silver and, optionally, oneor more promoters and, optionally, one or more co-promoters.

In general, a catalyst of the present invention may be prepared byimpregnating a carrier of this invention with silver and, optionally,one or more promoters, such as, for example, rare earth metals,magnesium, rhenium and alkali metals (lithium, sodium, potassium,rubidium and cesium), or compounds thereof, and, optionally, one or moreco-promoters, such as, for example, sulfur, molybdenum, tungsten andchromium, or compounds thereof. Among the promoter components that canbe incorporated into the carrier, rhenium and the alkali metals, inparticular, the higher alkali metals, such as potassium, rubidium andcesium, are preferred. Most preferred among the higher alkali metals iscesium, which may be used alone or in a mixture together with forexample potassium and/or lithium. Either the rhenium promoter may beused without an alkali metal promoter being present or an alkali metalpromoter may be used without a rhenium promoter being present or arhenium promoter and an alkali metal promoter can both be present in thecatalyst system. The co-promoters for use in combination with rheniumcan include sulfur, molybdenum, tungsten, and chromium.

Silver is incorporated into the carrier by contacting it with a silversolution formed by dissolving a silver salt, or silver compound, orsilver complex in a suitable solvent. The contacting or impregnation ispreferably done in a single impregnation step whereby the silver isdeposited onto the carrier so as to provide, for instance, at leastabout 8 weight percent silver up to about 30 weight percent, based onthe total weight of the catalyst. In another preferred embodiment asubstantially higher amount of silver is deposited onto the carrier, forinstance, at least 12 weight percent silver, based on the total weightof the catalyst, where the silver may be deposited in more than oneimpregnation step, for example in two, three or four impregnation steps.

The one or more promoters can also be deposited on the carrier eitherprior to, coincidentally with, or subsequent to the deposition of thesilver, but, preferably, the one or more promoters are deposited on thecarrier coincidentally or simultaneously with the silver. When thecatalyst comprises silver, rhenium and a co-promoter for rhenium, it maybe advantageous to deposit the co-promoter prior to or simultaneous withthe deposition of silver, and to deposit rhenium after at least aportion of the silver has been deposited. The advantage is this sequenceof deposition steps materializes in an enhanced stability of thecatalyst in particular in respect of its activity.

Promoting amounts of alkali metal or mixtures of alkali metal can bedeposited on a carrier using a suitable solution. Although alkali metalsexist in a pure metallic state, they are not suitable for use in thatform. They are generally used as compounds of the alkali metalsdissolved in a suitable solvent for impregnation purposes. The carriermay be impregnated with a solution of the alkali metal compound(s)before, during or after impregnation of the silver in a suitable formhas taken place. An alkali metal promoter may even be deposited on thecarrier after the silver component has been reduced to metallic silver.

The promoting amount of alkali metal utilized will depend on severalvariables, such as, for example, the surface area and pore structure andsurface chemical properties of the carrier used, the silver content ofthe catalyst and the particular ions and their amounts used inconjunction with the alkali metal cation.

The amount of alkali metal promoter deposited upon the carrier orpresent on the catalyst is generally in the range of from about 10 partsper million to about 3000 parts per million, preferably between about 15parts per million and about 2000 parts per million and more preferably,between about 20 parts per million and about 1500 parts per million, byweight of the metal relative to the weight of total catalyst.

The carrier can also be impregnated with rhenium ions, salt(s),compound(s), and/or complex(es). This may be done at the same time thatthe alkali metal promoter is added, or before or later; or at the sametime that the silver is added, or before or later. Rhenium, alkalimetal, and silver may be in the same impregnation solution. Theirpresence in different solutions will provide suitable catalysts, and insome instances even improved catalysts.

The preferred amount of rhenium, calculated as the metal, deposited onor present on the shaped agglomerate or catalyst ranges from about 0.1micromoles (μmole) per gram to about 10 micromoles per gram, morepreferably from about 0.2 micromoles per gram to about 5 micromoles pergram of total catalyst, or, alternatively stated, from about 19 partsper million to about 1860 parts per million, preferably from about 37parts per million to about 930 parts per million by weight of totalcatalyst. The references to the amount of rhenium present on thecatalyst are expressed as the metal, irrespective of the form in whichthe rhenium is actually present.

The rhenium compound used in the preparation of the instant catalystincludes rhenium compounds that can be solubilized in an appropriatesolvent. Preferably, the solvent is a water-containing solvent. Morepreferably, the solvent is the same solvent used to deposit the silverand the alkali metal promoter.

Examples of suitable rhenium compounds used in making the inventivecatalyst include the rhenium salts such as rhenium halides, the rheniumoxyhalides, the rhenates, the perrhenates, the oxides and the acids ofrhenium. A preferred compound for use in the impregnation solution isthe perrhenate, preferably ammonium perrhenate. However, the alkalimetal perrhenates, alkaline earth metal perrhenates, silver perrhenates,other perrhenates and rhenium heptoxide can also be suitably utilized.

The one or more co-promoters can be deposited on the carrier by anysuitable manner known to those skilled in the art. The co-promoter isdeposited on the carrier either prior to, coincidentally with, orsubsequent to the deposition of the silver, but preferably, the one ormore co-promoters are deposited on the carrier coincidentally orsimultaneously with the silver. A co-promoting amount of co-promoter isdeposited on the carrier and can generally be in the range of from about0.01 to about 25, or more, μmoles per gram of total catalyst.

The catalysts according to the present invention have a particularlyhigh activity and high selectivity for ethylene oxide production in thedirect oxidation of ethylene with molecular oxygen to ethylene oxide.For instance, the inventive catalyst can have an initial selectivity ofat least about 86.5 mole percent, preferably, at least 87 mole percentand, most preferably, at least 88.5 mole percent. It is a benefit ofthis invention that when packing the inventive catalyst into a catalystbed it provides a catalyst bed having a relatively high silver loading,without causing an increased pressure drop over the catalyst bed when inuse in the process for manufacturing ethylene oxide, and/or having animproved balance of packing density relative to such pressure drop. Whendecreasing the bore diameter, the balance of pressure drop/packingdensity behaves favorably in a typical reactor tube used in themanufacture of ethylene oxide, compared with predictions on the basis oftheoretical models, for example the Ergun Correlation, see W. J. Beekand K. M. K. Muttzall, “Transport Phenomena”, J. Wiley and Sons Ltd,1975, p. 114. By practicing the present invention, it is achievable thatthe silver loading of the catalyst may be at least 150 kg silver/m³catalyst bed, preferably at least 170 kg silver/m³ catalyst bed, morepreferably at least 200 kg silver/m³ catalyst bed, and in particular atleast 250 kg silver/m³ catalyst bed. Frequently, the silver loading isat most 800 kg silver/m³ catalyst bed, more frequently at most 600 kgsilver/m³ catalyst bed, still more frequently at most 550 kg silver/m³catalyst bed. The high silver loading permits the application ofrelatively mild conditions in the process for manufacturing ethyleneoxide, in particular temperature, for the achievement of a given workrate, along with the achievement of an improved selectivity and catalystlife, in particular in terms of activity stability and selectivitystability.

As it is used herein with reference to the selectivity of a catalyst,the term “selectivity”, Sw, means the mole percent (%) of the desiredethylene oxide formed relative to the total of ethylene converted. Theselectivity may be specified at a given work rate, w, for a catalystwith the work rate being defined as the amount of ethylene oxideproduced per unit volume of catalyst (e.g., kg per m³) per hour. As itis used herein with reference to the activity of a catalyst, the term“activity”, Tw, means the temperature needed to reach a given work rate.

The conditions for carrying out the epoxidation reaction in the presenceof the catalysts according to the present invention broadly comprisethose already described in the prior art. This applies, for example, tosuitable temperatures, pressures, residence times, diluent materialssuch as nitrogen, carbon dioxide, steam, argon, methane or othersaturated hydrocarbons, to the presence of moderating agents to controlthe catalytic action, for example, 1,2-dichloroethane, vinyl chloride,ethyl chloride or chlorinated polyphenyl compounds, to the desirabilityof employing recycle operations or applying successive conversions indifferent reactors to increase the yields of ethylene oxide, and to anyother special conditions which may be selected in processes forpreparing ethylene oxide. Pressures in the range of from atmospheric toabout 3450 kPa gauge (500 psig) are generally employed. Higherpressures, however, are not excluded. The molecular oxygen employed asreactant can be obtained from any suitable source including conventionalsources. A suitable oxygen charge can include relatively pure oxygen, ora concentrated oxygen stream comprising oxygen in major amount withlesser amounts of one or more diluents, such as nitrogen and argon, orany other oxygen-containing stream, such as air. The use of the presentcatalysts in ethylene oxide reactions is in no way limited to the use ofspecific conditions among those that are known to be effective.

For purposes of illustration only, the following table shows the rangeof conditions that are often used in current commercial ethylene oxidereactor units:

TABLE I *GHSV 1500-10,000   Inlet Pressure 150-400 psig Ethylene Oxide(EO) Production (Work Rate) 2-20 lbs. EO/cu. ft. catalyst/hr. Coolanttemperature 180-315° C. Catalyst temperature 180-325° C. O2 conversionlevel 10-60%  Inlet Feed Ethylene 1-40% Oxygen 3-12% Carbon dioxide0-15% Ethane 0-3%  Argon and/or methane and/or nitrogen balance Diluentchlorohydrocarbon moderator 0.3-20 ppmv total *Cubic feet of gas atstandard temperature and pressure passing over one cubic foot of packedcatalyst per hour.

In a preferred application, ethylene oxide is produced when anoxygen-containing gas is contacted with ethylene in the presence of theinventive catalysts under suitable epoxidation reaction conditions suchas at a temperature in the range of from about 180° C. to about 330° C.,and, preferably, 200° C. to 325° C., and a pressure in the range of fromatmospheric to about 3450 kPa gauge (500 psig) and, preferably, from1034 kPa to 2758 kPa gauge (150 psig to 400 psig). In the normalpractice of the process for manufacturing ethylene oxide, the feedstream which is contacted with the catalyst, and which comprisesethylene and oxygen, comprises in addition a low concentration of carbondioxide, because carbon dioxide is a byproduct of the process andappears, in part, in the feed stream as a result of recycling. It isadvantageous to reduce in the feed stream the concentration of carbondioxide to a low level, as this will further enhance the catalystperformance in terms of activity, selectivity and catalyst life. It ispreferred that the quantity of carbon dioxide in the feed is at most 4mole-%, more preferred at most 2 mole-%, in particular at most 1 mole-%,relative to the total feed. Frequently the quantity of carbon dioxidewill be at least 0.1 mole-%, more frequently at least 0.5 mole-%,relative to the total feed.

The ethylene oxide produced may be recovered from the reaction mixtureby using methods known in the art, for example by absorbing the ethyleneoxide from the reactor outlet stream in water and optionally recoveringthe ethylene oxide from the aqueous solution by distillation.

The ethylene oxide produced in the epoxidation process may be convertedinto ethylene glycol, an ethylene glycol ether or an alkanolamine.

The conversion into the ethylene glycol or the ethylene glycol ether maycomprise, for example, reacting the ethylene oxide with water, suitablyusing an acidic or a basic catalyst. For example, for makingpredominantly the ethylene glycol and less ethylene glycol ether, theethylene oxide may be reacted with a ten fold molar excess of water, ina liquid phase reaction in presence of an acid catalyst, e.g. 0.5-1.0% wsulfuric acid, based on the total reaction mixture, at 50-70° C. at 100kPa absolute, or in a gas phase reaction at 130-240° C. and 2000-4000kPa absolute, preferably in the absence of a catalyst. If the proportionof water is lowered the proportion of ethylene glycol ethers in thereaction mixture is increased. The ethylene glycol ethers thus producedmay be a di-ether, tri-ether, tetra-ether or a subsequent ether.Alternative ethylene glycol ethers may be prepared by converting theethylene oxide with an alcohol, in particular a primary alcohol, such asmethanol or ethanol, by replacing at least a portion of the water by thealcohol.

The conversion into the alkanolamine may comprise reacting ethyleneoxide with an amine, such as ammonia, an alkyl amine or a dialkylamine.Anhydrous or aqueous ammonia may be used. Anhydrous ammonia is typicallyused to favor the production of monoalkanolamine. For methods applicablein the conversion of ethylene oxide into the alkanolamine, reference maybe made to, for example U.S. Pat. No. 4,845,296, which is incorporatedherein by reference.

Ethylene glycol and ethylene glycol ethers may be used in a largevariety of industrial applications, for example in the fields of food,beverages, tobacco, cosmetics, thermoplastic polymers, curable resinsystems, detergents, heat transfer systems, etc. Alkanolamines may beused, for example, in the treating (“sweetening”) of natural gas.

The above description is considered that of particular embodiments only.Modifications of the invention will occur to those skilled in the artand to those who make or use the invention. Therefore, it is understoodthat the embodiments shown in the drawings and described above aremerely for illustrative purposes and are not intended to limit the scopeof the invention, which is defined by the following claims asinterpreted according to the principles of patent law, including theDoctrine of Equivalents.

1-27. (canceled)
 28. A process for preparing an olefin oxide by reactinga feed comprising an olefin and oxygen in the presence of a catalystcomprising a porous ceramic body, silver and one or more promotersuseful for the epoxidation of olefins, wherein said porous ceramic bodycomprises a first end, a second end, and a wall disposed between andintersecting said ends, said wall comprising at least three lobes and atleast three valleys formed in the length of the wall, each valleylocated between two of said three lobes, said lobes rounded at theintersection of said first end and said wall, and said valleys notrounded at the intersection of said first end and said wall.
 29. Theprocess as claimed in claim 28, wherein the olefin comprises ethylene.30. A process for preparing a 1,2-diol, a 1,2-diol ether, a1,2-carbonate, or an alkanolamine comprising converting an olefin oxideinto the 1,2-diol, the 1,2-diol ether, the 1,2-carbonate, or thealkanolamine, wherein the olefin oxide has been prepared by reacting afeed comprising an olefin and oxygen in the presence of a catalystcomprising a porous ceramic body, silver and one or more promotersuseful for the epoxidation of olefins, wherein said porous ceramic bodycomprises a first end, a second end, and a wall disposed between andintersecting said ends, said wall comprising at least three lobes and atleast three valleys formed in the length of the wall, each valleylocated between two of said three lobes, said lobes rounded at theintersection of said first end and said wall, and said valleys notrounded at the intersection of said first end and said wall.